This invention pertains to a power drive unit utilizing a hydraulic power supply for operation of a structure by a fluid-operated hydraulic motor and which places different loads on the motor during a cycle of operation and having means sensing the load on the motor to set the motor displacement at the least value possible for the load condition on the motor.
Power drive units having a hydraulic fluid supply have many different uses with one particular use being in the aircraft field where the unit is utilized for powering aircraft engine structure, such as thrust reversers which must be moved between stow and deploy positions. Power driven units have included air motors for operation of such structure and the prior art also includes the use of a hydraulic bi-directional motor, with the motor having a fixed displacement.
In operation of certain structure, such as thrust reversers, there are varying torque demands on the motor during the cycle of operation and in using a fixed displacement motor, the motor must be set to an adequate displacement to provide the necessary maximum torque requirement and with the fixed displacement and constant hydraulic fluid supply it is not possible to provide for increased speed of the motor when there are lesser torque demands on the motor.
The prior art includes a power driven unit having a hydraulic power supply and which has a system for operating thrust reverser structure in stow and deploy cycles. An axial piston motor has a wobbler which is set in one displacement position in one of the stow-deploy operations and which is set in another, or one of two different other displacement positions, in the other of said operations. This prior art unit does not optimize the displacement of the motor at all times to always maintain only the minimum displacement required for the necessary torque during all operations provided by operation of the motor in both directions. This system is shown in an application of Allyn M. Aldrich, entitled "POWER DRIVE UNIT," Ser. No. 900,312, filed Apr. 26, 1978.